1. Field of the Invention
The present invention relates to a composition of a sensor element, a temperature sensor and a method of manufacturing the temperature sensor having the composition of the sensor element. More particularly, the present invention relates to a composition for a sensor element having improved accuracy and thermal stability in sensing temperature, and a temperature sensor, wherein wires are inserted into a sensor element, comprising the same composition and which has heat resistance, impact resistance, vibration resistance, durability and the like to perform temperature sensing at a high temperature and under a vibration condition; and a method for manufacturing the temperature sensor.
2. Description of the Related Art
Recently, as restrictions on environmentally harmful gases from vehicles increase, systems are being developed for a gas reducing device for vehicles. Particularly, in diesel vehicles, nitrogen oxides (NOx) and the like are generated during fuel combustion. For example, diesel vehicles may emit particulate matter (PM) of less than 0.005 g per 1 km, and to regulate this exhaust, a DPF (Diesel Particulate Filter) system as an exhaust gas reducing device may be used. The DPF system installed in an exhaust collects particulate matter in the exhaust gas using a catalyst filter and controls a regeneration process combusting the collected PM when certain condition is satisfied.
Moreover, the regeneration process is conducted at a temperature for optimum efficiency (e.g., at the temperature where the particulate matter collected in the filter is combusted). To accomplish this process, an accurate and durable temperature sensor must be installed in the DPF system. Further, the temperature sensor is installed in a combustion device and related parts commonly used for vehicles, to accurately sense temperature at any temperature, and to maintain normal vehicle operation with strong impact resistance and durability.
The temperature sensor is a device configured to sense temperature using the change of material density, resistance, electromotive force and the like according to temperature, and the temperature sensor includes a thermocouple, a resistance temperature detector, a thermistor (NTC) thermometer and the like. The thermocouple thermometer is a thermometer using thermal electromotive force of a thermocouple, and it measures temperature by thermal electromotive force value, which is generated according to a changing temperature of one contact point when both ends of two metal wires are connected and the other contact point is maintained to a fixed temperature. Further, the resistance thermometer bulb is a device measuring temperature by resistance value using the change of electric resistance of metal or semiconductor according to temperature. The thermistor thermometer is generally manufactured by sintering metal oxides, and the thermistor is a device changing electric resistance according to the change of temperature.
The thermistor thermometer is classified into a PTC (Positive temperature coefficient) thermistor and a NTC (Negative temperature coefficient) thermistor. The PTC thermistor increases resistance value according to an increasing temperature, and the NTC thermistor decreases resistance value according to an increasing temperature.
The temperature sensor used for the exhaust system of a vehicle should be operated at the temperature of about 500° C. or higher, and should have thermal shock resistance resisting repetitive temperature change between high temperature and room temperature, and vibration resistance and impact resistance resisting extreme vibration often generated during vehicle running.
Conventional temperature sensors generally comprise a sensor element and lead wires, and the sensor element is commonly manufactured with metals or metal oxides. Conventionally, the metal oxides are insulators, but when transition metal oxides are mixed therewith and are sintered, they have semiconductive conductivity. Particularly, the temperature sensor used at a high temperature prepared through a ceramic process by mixing a composition for a sensor element comprising transition metal oxides such as Fe2O3, NiO, Cr2O3, MnO2 and the like, calcining and sintering the composition, may reduce accuracy of sensing temperature due to error caused by thermal stability reduction at 500° C. or higher and low resistance as several ohms.
Moreover, the conventional temperature sensor is manufactured by printing or gilding paste electrodes of silver (Ag), gold (Au), platinum (Pt) and the like on the surface of the sensor element, and attaching lead wires or pins of nickel (Ni), Pt, Au, copper (Cu) and the like thereon, and when the surface electrodes are used, the lead wires or pins can easily be separated from the element surface and disconnected at a high temperature or under extreme vibration.
The description provided above as a related art of the present invention is for helping understanding the background of the present invention and should not be construed as being included in the related art known by those skilled in the art.